In various locations in the ocean, and in particular in a large area in the central Pacific Ocean to the South of the Hawaiian Islands, polymetallic nodules exist in a muddy surface layer on the bottom of the deep sea. The size of the nodules varies from pebble size to first size and generally lie in water depths of around 5000 meters.
Since the late 1970's, there have been various attempts to engineer a commercially viable solution to mine the nodules from the deep ocean seafloor.
One prior art solution is described in U.S. Pat. No. 4,042,279. This solution comprises a seafloor nodule recovery vehicle and an ore hoisting system to transport ore from the seafloor nodule recovery vehicle to a surface vessel.
The seafloor nodule recovery vehicle described in U.S. Pat. No. 4,042,279 is of a category of vehicles referred to as benthic sleds. Benthic sleds are typically unable to move under their own power nor do the sleds have the ability to steer. In the system described, the seafloor nodule recovery vehicle and associated ore hoisting system is towed along by the surface vessel and collects nodules from the seafloor adjacent an underside of the recovery vehicle. The nodules, in a slurry, are then pumped from the recovery vehicle to the ore hoisting system, in this case a riser pipe.
The solution described in U.S. Pat. No. 4,042,279 has various disadvantages. Whilst the seafloor nodule recovery vehicle is effective enough in collecting the nodules from the seafloor and communicating the collected nodules to the ore hoisting system, the seafloor nodule recovery vehicle is unable to steer to follow a predetermined path and tends to “snake” as it travels due mostly to drag on, and vortex shedding off, the riser pipe. This effect worsens with increased speed through the water.
In circumstances where the seafloor nodule recovery vessel is operating in depths of around 5000 meters, this inability to maintain a desired path greatly reduces the recovery rate of nodules from the seafloor.
A further disadvantage of the system described in U.S. Pat. No. 4,042,279 is the cost associated with the surface vessel and the ore delivery system. The surface vessel needs to be large enough to have a riser system extending towards the seafloor of a length sufficient to deliver the ore to the surface vessel.
The weight associated with a riser system of this scope is significant and thus the surface vessel needs to be of a size to carry that weight. This leads to very high operating costs in circumstances where the seafloor nodule recovery vessel is only able to recover a relatively small amount of nodules in any given time period.
Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.